Electrochemical Conversion of CO2 into Formate Boosted by In Situ Reconstruction of Bi-MOF to Bi2O2CO3 Ultrathin Nanosheets

Substantial emissions of CO₂ have presented formidable challenges for global climate dynamics. Electrochemical reduction of CO₂ to produce formic acid (HCOOH) is considered to be a promising approach for achieving carbon neutrality. Nevertheless, the development of a catalyst exhibiting both high catalytic activity and selectivity toward desired products remains an arduous task. Herein, we report the synthesis of a unique porous bismuth-based MOF (Bi-BTC) through microwave-assisted agitation. The Bi-BTC MOF has a good catalytic performance in electrochemical CO₂RR to formate products. At -0.9 V (vs RHE) potential, the Faradaic efficiency of formate can reach 96%, and the current density of the CO₂RR is 25 mA/cm². Bi-BTC also exhibits good electrochemical stability. FE_formate and current density were maintained for 24 h with almost no attenuation. It was found that Bi-BTC was reconstructed in the CO₂RR process. The shape of nanocolumn before electrolysis is transformed into an ultrathin nanosheet. The soft and hard acid-base theory (HSAB) proves that the reason for the reconfiguration is that the hard base ions (HCO₃^-) and the intermediate acid (Bi³⁺) break in the Bi-O bond in Bi-MOF, resulting in the transition of the original column structure of Bi-BTC to Bi₂O₂CO₃ ultrathin nanosheeets. The DFT calculation shows that the restructured Bi₂O₂CO₃ nanosheet exposes a crystal surface structure, which is conducive to lower the activation energy barrier of the electrochemical CO₂RR intermediate *OCHO and stabilizing the reaction intermediate. Therefore, it is more beneficial to improve the selectivity of the electrochemical CO₂RR to formate formation. This result proves that irreversible reconfiguration of catalyst is beneficial to electrochemical CO₂RR. In addition, coupling a Bi-BTC cathode with a stable anode (IrO₂) enables battery-driven high-activity CO₂RR and an OER with good activity and efficiency.